1. Field of the Invention
The present invention relates to an image forming device such as a laser printer, a digital photocopier and the like. More particularly, the present invention relates to a transfer unit-fixing apparatus to integrally fix a transfer unit to a door of an image forming device, and an image forming device having the transfer unit-fixing apparatus.
2. Description of the Related Art
In general, an image forming device such as an electrophotographic tandem color image forming device has a plurality of developing units and a plurality of photosensitive body units disposed in parallel. Each of the plurality of photosensitive body units has a photosensitive body to form a toner image of a particular color, such as yellow, magenta, cyan and black, which is developed by a corresponding one of the plurality of developing units. A transfer unit transfers the toner images formed on the photosensitive bodies onto a recording medium, such as a sheet of printing paper, and a fusing unit fuses and fixes the toner images transferred onto the recording medium with heat and pressure.
Another type of tandem color image forming device further comprises an intermediate transfer unit having a transfer drum or a transfer belt disposed between the photosensitive bodies and the transfer unit. In this case, the toner images formed on the photosensitive bodies are not directly transferred to the recording medium, but instead are first transferred onto the transfer belt and then retransferred from the transfer belt onto the recording medium.
Tandem color image forming devices having a plurality of photosensitive body units that form a required image by simultaneously revolving the plurality of photosensitive bodies are advantageous in that they can produce color images at high speeds, as compared with a color image forming device that has a single photosensitive body unit that forms a required image by revolving a single photosensitive body several times. The construction of an apparatus with a plurality of photosensitive body units and developing units is complicated, however, and it is preferable that a tandem color image forming device is easily assembled, maintained and repaired.
Accordingly, a tandem color image forming device, for example a tandem color laser printer 1 as illustrated in FIG. 1, generally does not have separate photosensitive body units 22 and corresponding developing units 28. Instead, the photosensitive body units 22 and corresponding developing units 28 are contained in a plurality of cartridges 11Y, 11M, 11C, 11K. In other words, the components are modular so that they can be mounted in or removed from a cartridge frame 29 of a main body 10 as a single cartridge unit.
Also, as illustrated in FIGS. 1 and 2, a transfer unit 17 is integrally formed with a door 19 to be movable therewith, and is provided with a transfer belt or a medium conveying belt 18. The medium conveying belt 18 contacts the photoconductive bodies 14 of the photosensitive body units 22 in the plurality of cartridges 11Y, 11M, 11C, 11K when the door 19 is moved from the open position illustrated in FIG. 2 to the closed position illustrated in FIG. 2 by being rotated about a rotation axis 23.
However, in the conventional tandem color laser printer 1 as constructed above, the transfer unit 17 is fixed and assembled to the door 19 by fixing means such as screws, and therefore is integrally formed with the door 19. Thus, when the transfer unit 17 is assembled to the door 19 during manufacturing, fixing operations are required. These fixing operations may be problematic and require considerable time during assembly.
Also, to form a uniform image, it is important that the medium conveying belt 18 is maintained in contact with the photoconductive bodies 14 of the photosensitive body units 22 in the plurality of cartridges 11Y, 11M, 11C, 11K at a predetermined pressure to form predetermined nips therebetween. However, the conventional tandem color laser printer 1 is usually configured so that the cartridges 11Y, 11M, 11C, 11K mounted in a cartridge frame 29 and the transfer unit 17 fixed to the door 19 come in contact with each other when the door 19 is closed. Thus, if the cartridge frame 29 and the door 19 are not accurately manufactured due to manufacturing tolerances and the like, or are twisted due to contractions or expansions caused by external forces or changes in the environment, the medium conveying belt 18 may not contact the photoconductive bodies 14 at the appropriate predetermined pressure and therefore may not properly form the predetermined nips. Also, during image forming operation, the process speed of the cartridges 11Y, 11M, 11C, 11K and the transfer unit 17 may change. In this case, when toner images are transferred in turn onto a recording medium P from the photoconductive bodies 14 by the medium conveying belt 18 of the transfer unit 17, image defects such as jitter, mis-registration, skew and the like may be produced on the resultant image formed on the recording medium P.
Also, the conventional tandem color laser printer 1 is not provided with a separate relative position fixing means to maintain a fixed relative position between the cartridges 11Y, 11M, 11C, 11K and the transfer unit 17. Instead, the relative position between the cartridges 11Y, 11M, 11C, 11K and the transfer unit 17 is determined by a locking means (not shown) which locks the door 19 to a main body 10.
Accordingly, if the door 19 having the transfer unit 17 assembled thereto, or the locking means for locking the door 19 to the main body 10, are not accurately manufactured due to manufacturing tolerances and the like, the fixing position of the transfer unit 17 is directly affected, and therefore the transfer unit 17 may not be arranged at the proper position. Also, if during the image forming operation of the printer, a force is imparted on the door 19 by an external source, or vibration is generated by the cartridges 11Y, 11M, 11C, 11K and the transfer unit 17, the transfer unit 17 is directly affected. In this case, the position of the transfer unit 17 relative to the cartridges 11Y, 11M, 11C, 11K may change, and image defects such as jitter, mis-registration, skew and the like may be produced on the resultant image formed on the recording medium P.
Accordingly, there is a need for an improved apparatus for fixing a transfer unit to a door.